1. Field of Invention
The present invention relates to an electrophoretic dispersion and electrophoretic devices including the same. The present invention particularly relates to an electrophoretic dispersion containing a liquid dispersion medium and electrophoretic particles, dispersed in the medium, including at least coloring means and a resin portion and relates to an electrophoretic device including a pair of electrodes and the electrophoretic dispersion disposed between the electrodes.
2. Description of Related Art
Conventionally, electrophoretic display systems including electrophoretic devices are known. The electrophoretic devices each include a pair of electrodes and an electrophoretic dispersion disposed between the electrodes, wherein the electrophoretic dispersion contains a liquid dispersion medium and electrophoretic particles. In such electrophoretic devices, the distribution of the electrophoretic particles is changed when a voltage is applied between the electrodes. The electrophoretic display systems display an image using such a phenomenon.
Each electrophoretic display system includes the electrophoretic devices each including a pair of substrates and an electrophoretic dispersion placed between the substrates, wherein at least one of the substrates comprises a transparent material, the substrates have a predetermined distance therebetween, and the electrophoretic dispersion contains at least a liquid dispersion medium and electrophoretic particles having a surface charge. When a voltage is applied between the substrates, the electrophoretic particles electrophoretically migrate depending on the surface charge and the direction of the electric field, thereby changing the distribution of the electrophoretic particles. Therefore, the color of the electrophoretic device is changed when viewed from the transparent substrate side. Thus, a desired image can be displayed by controlling the amount of a voltage being applied.
Such an electrophoretic display system is disclosed in Japanese Unexamined Patent Application Publication No. 1-86116. The electrophoretic display system includes a pair of substrates and microcapsules, disposed therebetween, containing an electrophoretic dispersion. The electrophoretic dispersion contained in the microcapsules can be easily handled. However, in the above electrophoretic display system, there is a problem in that electrophoretic particles are settled due to a large difference in density between the liquid dispersion media and the electrophoretic particles. In order to solve such a problem, the following method is provided: electrophoretic particles having cavities therein are used for obtaining a small difference in density between the liquid dispersion media and the electrophoretic particles, thereby preventing the settlement.
For example, a capsule electrophoretic particle of a microballoon type is disclosed in Japanese Unexamined Patent Application Publication No. 48-31097, wherein the particle contains gas.
The following technique is disclosed in Japanese Unexamined Patent Application Publication No. 2-24633: a core for electrophoretic particles is formed using a porous organic material and the core is coated with an inorganic material, thereby adjusting the density.
Furthermore, techniques relating to the following particles are disclosed in Japanese Unexamined Patent Application Publication 2000-227612: a fine particle having a pigment component thereon and cavities therein, another fine particle including a pigment component thereon and a hollow organic polymer, and another fine particle including a pigment component having cavities therein.
However, in these conventional techniques, there is a problem in that it is difficult to control the number and the volume of cavities in each electrophoretic particle and therefore it is difficult to minutely control the density of the electrophoretic particle with preciseness. That is, since the microbaloon-type capsule particle and the particle including the pigment component thereon and the hollow organic polymer have a single cavity, the conditions of the manufacturing steps must be precisely adjusted in order to minutely control the density of the particles with preciseness. Furthermore, in the particle having the core comprising porous organic material, it is difficult to control the number and the total volume of cavities in the organic material in the manufacturing steps.